Apparatus for burning fuel



rch 24, 1936. F. D. HOFFMAN 2,034,812

APPARATUS FOR BURNING FUEL Filed Sept. 25, 1951. 3 Sheets-Sheet 2 March24,1936 F, D HOFFMAN 2,034,812

APPARATUS FOR BURNING FUEL Filed Sept. 25, 1931 s Sheets-Sheet is F 216 46 45 I 7; Z2

My 5' 4 I I [M M l4 l4 /4 x /4 Flifi 7 FfIfio g Jvvuentot Patented Mar. 24, 1936 Combustion Laboratories,

Inc.,

Painesville, Ohio, a corporation of Ohio Application September 23, 1931, Serial No. 564,538

3 Claims.

This invention relates to an apparatus for burning coal, coke and other solid fuels, and is particularly concerned with an improved aerator by which I am able to obtain complete com- 5 bustion of the fuel and eifectively utilize the resultant heat.

By the use of known methods and apparatus for burning solid fuels a large percentage of the heat units are wasted. Part of this loss results 10 from imperfectly freeing the volatile and inflammable content of the fuel and part from the escape of unburned gases. These and other losses and the manner in which they reduce the efficiency of combustion and the consequent deleterious effects of improper combustion on the furnace and apparatus are more fully described in my copending application Ser. No. 564,537 filed September 23, 1931.

In my copending application I have described 2.0 a method of burning solid fuels and an aerator or aerating grate adapted for carrying out my process. The present invention has to do with a modified method and somewhat different aerator, which is better suited for use in large fur- 25 naces, for example, such as furnaces for steam heating and power plants.

An object of this invention is the efficient combustion of solid fuels and economical utilization of resultant heat and the accomplishment of 30 these objects with apparatus which may be economically manufactured.

Another object of my invention is to maintain a firebed having a large heat radiating surface for effectively utilizing the heat units of the fuel 35 and shaped to direct the radiated heat against the combustion chamber walls.

Another object of my-invention is the complete combustion of cheap low grade fuels and consequent elimination of smoke and reduction of cinders or ash residue.

Another object of my invention resides in the fact that the rate of burning of the fuel may be accurately controlled throughout a wide range and instantaneous circulation of air and gases ob- 45 tained so that heat may be quickly increased or decreased.

A very important object of my invention is to correlate the rate of evolution of gases from the fuel and the volume and distribution of air 50 to cause complete aeration and burning of the fuel, and to mix preheated air with the evolved gases so that all combustible gas is burned quickly and the cooling or conveying effects of excessive air are eliminated.

55 Another more specific object is to volatilize the fuel and burn the resultant gases close to the fuel bed and to maintain combustion of the fuel against the walls of the combustion chamber.

Still another object of my invention is to maintain the undersurface and uppersurface of the 5 fuel bed in a shape which causes efficient burning of the fuel and application of the heat.

Another object of my invention is the recuperation of heat from the grate bars and other parts of the apparatus beneath the fuel bed.

Another object of my invention is to humidify the air and increase its convectivity and to hydrogenize the evolved gases.

The aerator with which my invention is particularly concerned may be easily and quickly in- IE5 stalled in any of the furnaces of the present type with slight or no change in the furnace structure.

Another object of my invention is an aerator which may be effectively used in combination with mechanical overfeed stokers and will effectively distribute the fuel in the combustion chamber.

A-decided advantage of my invention is that free circulation of air and gases in the furnace is maintained at all times and the danger of explosion of accumulated gases is entirely eliminated.

Other objects and advantages will become apparent from the following specification in which reference is made to the drawings by the use of numerals, the same numerals being used to designate the parts in the various views.

In the drawings which illustrate a form of my apparatus suitable for carrying out my process:

Fig. l is a vertical sectional view through a furnace showing my aerator installed in operating position;

Fig. 2 is a partial sectional view of the furnace and aerator illustrated in Fig. 1, taken on a plane indicated by the line 2-2, Fig. 1;

Figs. 3 and 4 are respectively side elevation and a plan view of my aerator.

Fig. 5- isa sectional view of the aerator taken on a plane indicated by the line 5-5, Fig. 4;

Figs. 6 and 7 are sectional views of the aerator taken respectively on planes indicated by the lines 66 and 1-'l of Fig. 3.

By way of illustration I have shown a form of my aerator installed in a furnace of the hot water heating type. This furnace comprises a combustion chamber 2 spanned at the bottom by grate 4, upon which the fuel is supported. The combustion chamber of the furnace is formed by a plurality of frame-like water jackets-placed face to face and interconnected. The rear end of the furnace may be closed by a water jacket covering the entire wall. Thus Water may be brought close to the fuel bed and a large heating area provided, the walls of the combustion chamber substantially being formed by the Water jackets 6 which communicate with each other and with the other portions of the boiler. These water jackets may be formed so as to present as large a surface as possible to the interior of the combustion chamber. The entire furnace and boiler is covered with heat insulating material as illustrated for protection of the building in which it is installed and to reduce radiation losses.

The furnace is preferably positioned over an ash pit [9 which is in the form of a closed chamber, and is provided with a door 8 for feeding fuel thereinto. The chamber ill communicates with the outside air or with a forced draft of air through a suitable opening, a door of register l2 being provided for closing or regulating the size of the opening to control the amount of air being admitted. The aerator proper consists of an elongated shell or hoodlike grate having a substantially horizontal base l4 and grated side walls It. The side walls converge upwardly from the base and terminate in a top wall l8. In the form illustrated the side walls extend inwardly at about 60 to the horizontal.

The aerator is roughly wedge shaped in a vertical section, as better illustrated in Figs. 3 and 5; the small front wall 28 sloping upwardly rearwardly from the base, preferably at an angle of more than 45 from the horizontal. The front end wall 26 joins the top wall l8 near the front end of the base forming substantially a continuation thereof. The top'wall i8 slopes upwardly rearwardly at a comparatively small angle from the horizontal depending on the length and depth of the combustion chamber. In the chamber illustrated the slope is about 5 to 15 from the horizontal. Both the front wall 253 and the top wall are grated, preferably with longitudinally extending passages. The grated portion of the top wall terminates short of the rear end of the aerator, the rear portion being provided with a large unobstructed passage as indicated at 22. Resting on the top wall I8 over the opening 22 is a smaller shell or supplementary hoodlike head 24 having a top wall 26 which is preferably solid and forms a feeding or coking plate.

In the form illustrated in Fig. 4, the hood 24 is the same width as the top wall 58 and may be substantially square in outline. Lugs 25 may be provided on the top wall l8 about the opening 22 for retaining the hood 24 in proper position. The side walls 28 of the hood 24 may be vertical or sloped somewhat and are grated to permit passage of air. The front Wall 30 of the head 24 slopes upwardly and rearwardly from the top wall I8 to the top Wall 26. A form of hood which has proven effective is illustrated, the front wall 30 which is about half the length of the hood intersecting the top wall of the hood at an angle of approximately 45. The front wall is likewise in the form of a grating. The grated walls of both the large hood and supplementary head act as tuyeres for introducing air into the combustion chamber of the furnace.

When installed in the furnace the aerator may rest directly on the grates 4 of the'combustion chamber 2 or may be supported on legs 32 as ashes from the fuel bed will tend to fill the lower portion of the combustion chamber. The rear ends of both shells are open and when the aerator is thus installed lie against the walls of the combustion chamber, the aerator being aligned with the feeding door l2. Thus the walls of the combustion chamber may form a rear or closing wall of the aerator. The overall height of the aerator is such as to bring the top wall 26 of the shell 24 about even with the feeding door of the furnace. The aerator may extend longitudinally almost the entire length of the combustion chamber and laterally the wide base portion of the aerator may extend comparatively close to the walls of the combustion chamber as illustrated in Figs. 1 and 2. Both the height and length of the aerator may be varied somewhat as also may be the shape and slope of the walls, the amount of variation being apparent from the description of operation.

A steam conduit 34 is arranged to discharge into the chamber l8 preferably near the underside of the grates 4 as illustrated in Fig. 1, and is connected to a suitable source of steam so as to deliver a jet of steam along theunderside of the grates for purposes later to be described.

As above mentioned, the opening 22 communicates the space defined by the aerator and the rear wall of the combustion chamber with the hood 24 and through the grating thereof with the remainder of the combustion chamber so that a free unobstructed passage is formed.

Coal is fed into the combustion chamber through the door 8 onto the top 26 of the hood 24, or may be thrown onto the sloping wall N3 of the aerator. When the aerator is used with a mechanical stoker the former method is preferred, the coal being gradually fed onto the plate 26 and shoved off as more coal is fed into the furnace. As soon as the coal drops off of the hood 24, it travels down the side walls i5 and is thus spread outwardly. Part also passes down the sloping front wall 38 of the hood 24 and onto the top wall l8. Due to the sloping of the top wall 13 the coal moves continuously as it is fed thereon part of it traveling out over the sloping sides I6 and spreading. As indicated by the dotted lines 36 in Fig. l and the dotted line 38 of Fig. 2, the upper surface of the fuel bed is approximately the shape of the aerator and lies in a comparatively evenly distributed layer over the walls of the aerator. In this manner a fuel bed of much larger surface area is provided. Furthermore the fuel bed is of comparatively even thickness throughout the combustion chamber and has a large area exposed to the grated walls of the aerator and a large radiation surface substantially normal to the walls of the combustion chamber.

When the understraturn of the fire bed is in a state'of combustion the air passes into the chamber l E), and since it is comparatively cool tends to pass along the bottom thereof as indicated by the arrows 4i! and travels to the rear end of the chamber In and is deflected upwardly passing under the grates 4.

Since a free and unobstructed passage is provided from this chamber l0 underneath the aerator and hood 24, the air rises freely and a large portion of it passes out of the tuyere opening in the head 24. During its passage along this path the air is heated by contact with and radiation from the heated walls of the aerator and the heated grates of the furnace. Consequently it rises rapidly creating a considerable draft. Part of the air infiltrates into the fuel bed through the grated walls of the aerator as indicated by the arrows 42 in Fig. 1 and arrows 44 in Fig. 2. The

. degree.

remainder of the air passes up through the opening 22 into the hood 24 and out through the yres as described. A part of this air stream is directed laterally as indicated by the arrows 45 in Fig. 2 and part is directed forwardly, as indicated by the arrows 48 in Fig. 1. In this manner fuel tends to burn in a direction normal to the walls of the aerator, the air passing through the fuel bed in such direction. The remainder of the air being greatly preheated is directed across the top of the fuel bed. As a result the gases evolved from the fuel are driven laterally against the walls of the combustion chamber and forwardly through the furnace and against the end wall of the combustion chamber, being held close to the fuel bed by the inrushing stream of air.

Since this air is preheated however, the gases burn very rapidly and before they have passed out of the combustion chamber. Most of the gases are burned while held in actual contact with the combustion chamber walls. As a result of the shape of the upper surface of the fuel bed, a large area of radiation is provided and the radiation is in a direction approximately normal to the walls of the combustion chamber.

Thus very efficient combustion of the fuel is obtained and the heated gases are conveyed against the walls of the combustion chamber and burned thereagainst so that the furnace does not depend entirely upon radiation for heat. In furnaces of this type, however, one of the greatest difiiculties arises in maintaining the fuel in a state of combustion against the cold water jacketed walls of the combustion chamber. The tendency in ordinary furnaces is for the cold walls to lower the temperature of the adjacent fuel to such a degree that volatilization and ignition of the gases thereagainst is impossible.

In the ordinary furnace there is no tendency for the air currents to maintain the fuel in a state of combustion against the walls. Another reason for this resides from the fact that the air must pass through a large amount of fuel and consequently tends to localize at the thinnest part of the fuel bed which is usually at the center where combustion is more rapid and the fuel burns out more quickly. As a result the air does not pass close to the walls. If sufficient air is added to penetrate to the wall sides too heavy a blast is usually created in the center and too heavy a fire is maintained. By shaping the fuel bed in the manner herein described and maintaining it at practically constant thickness I am able to maintain the entire fuel bed in a practically even state of combustion, and, since the fuel bed is comparatively narrow between the aerator and the water jacket walls of the combustion chamber and there is free access of air thereinto, I am able to maintain combustion directly against the walls of the furnace and carry the evolved gases into contact therewith so that heat is most effectively applied.

In this manner I have been able to completely burn evenly all of the fuel rapidly with a very high degree of heat or slowly with a very low Obviously as the air is increased a larger portion is bypassed through the fuel and over and close to the fuel bed so that the amount of combustion and rate of volatilization of the fuel and the amount of preheated air directed into the gases is always correlated to give a proper mixture and eflicient combustion.

In some cases I desire to obtain a higher degree of heat, in which case a very fine mist or jet of steam is directed into the fuel preferably close to the grates 4. This steam or vapor rises immediately under the aerator and tends to expand thereunder, thus increasing the draft and causing a more forceful current of air across the top of the fuel bed and through the fuel bed. The steam or vapor likewise is heated by its contact with the under surface of the heated aerator and upon contact with the heated Walls and coals tends to break up and hydrogenize the gases and to form a Water gas. This gas produces. much greater heat than the hydrogen adding its. heat to the evolved gases.

Obviously since the by-passed air and the air directed through the fuel bed may be kept in a given portion combustion may be maintained at a given rate by regulating the draught through the door [2 and a check damper in the stack is not necessary.

In ordinary furnaces since air admitted to maintain combustion must all pass through the fuel bed, there is not enough to mix with the evolved gases and burn the same and gases accumulate in the furnace and become a dangerous or explosion fire hazard. In the furnace such as described, however, there is always a free circulation of air and the gases evolved are continuously burned.

It will be apparent therefore that the slope of the various walls of the aerator is dependent somewhat upon the length of the combustion chamber with which associated and the side walls are preferably sloped relative to the combustion chamber walls, so that no matter in what direction measured, the fuel bed is practically the same thickness. Likewise the aerator should extend close to the end of the fuel chamber so that the fuel bed is not disproportionately thick at the end of the chamber. By making the aerator walls with a slope instead of vertical the air is better directed therethrough and the entire combustion chamber does not have to be filled level with the top of the aerator thus thickened in a vertical plane.

The changes which may be made in the main body and the hood 24 to use the aerator effectively in a given furnace will be obvious from the operation described, the general principles being the same as herein set forth.

Having thus described my invention, I claim:

1. An apparatus for burning solid fuels which consists of a combution chamber having a grated bottom and a passage for feeding fuel thereinto and a register for introducing air beneath the grates, an aerator within said combustion chamber adjacent to said passage and extending from said fuel passage substantially to the end of the combustion chamber and terminating laterally close to the side walls of said combustion chamber, the walls of said shell sloping downwardly from said door and having openings therein, said walls terminating rearwardly and upwardly in a head member having passages communicating with a space beneath said aerator and with said combustion chamber.

2. The combination with a combustion chamber having a passage for introducing fuel thereinto of an aerator extending substantially the length of the chamber and having upwardly converging substantially parallel evenly spaced side walls, the walls of said aerator at the widest portion thereof lying close to the walls of said combustion chamber and a rearwardly sloping top wall inclined from the horizontal at a less angle than the side walls, and having a passage at the upper portion of said top wall and communicating the combustion chamber and the space beneath said aerator, a grated hood on said top wall and disposed over said passage, the top of said hood lying in a plane close to the bottom of the fuel passage of the combustion chamber.

3. In a device of the class described adapted for use with a heating apparatus having a combustion chamber provided with grates at the bottom thereof, a passage for feeding fuel thereto, and having means to introduce air beneath the grates, the device comprising a hollow body having an open bottom extending across the grate to receive air passing through the grate, said body extending from a point adjacent the door to a point adjacent the opposite side of the combustion chamber, the hollow body having an upper wall sloping downwardly from a point adjacent the fuel door to a point adjacent the opposite end of said body, the body having side walls diverging downwardly, the walls of said body having passages therethrough communicating with the interior of said hollow body, a head member associated with said hollow body and ex,- tending upwardly therefrom, the head member having passages therethrough communicating with the interior of the hollow body and with the combustion chamber at a point above the normal level of the top of the fuel bed, whereby a portion of the air introduced beneath the grates is conducted through the chamber in the hollow body and is introduced into the combustion chamber above the level of the fuel bed and is mixed with the gases emitted from the fuel bed.

FRED D. HOFFMAN. 

